System and method for removal of material

ABSTRACT

Apparatus for removal of material in reactions having limited solubility and diffusion. An exemplary system removes unwanted material from the surface of a semiconductor wafer. 
     A flow apparatus is provided for removal of material from a work piece having at least one reaction region containing removable material. The apparatus may include first and second assemblies positionable in spaced-apart relation to form a zone extending between the two assemblies for movement of gaseous material. The first assembly may include a fixture positioned to receive the work piece with the reaction region of the work piece disposed in the zone to allow movement of the gaseous material thereover. A flow assembly is configured to transfer into the zone a gas comprising a condensable material and a reacting species. 
     In another embodiment a system for removal of material from a workpiece includes a chamber, a flow component and a support apparatus. The flow component is configured to pass gaseous material into the chamber at a selectable rate and allow exit of liquid and gaseous materials from the chamber. The support apparatus is configured to position the workpiece thereon with the surface region of the work piece oriented for contact with gaseous material passed into the chamber by the flow component. The system may further include a thermal control configured to provide a differential temperature between a portion of a work piece and gaseous material passed into the chamber.

RELATED APPLICATIONS

This is a conversion of provisional application Serial No. 60/165,542filed Nov. 15, 1999. This application is related to Ser. No. 09/712,517[Higashi 14] filed on even date herewith.

FIELD OF THE INVENTION

The invention relates to cleaning processes of the type incorporatingsoluble oxidants and, in preferred embodiments, relates to removal ofphoto-resist (PR) and associated by-products during the cleaning stagesof integrated circuit manufacture.

BACKGROUND

It is well known that gas solubilities in liquid media such as water candecrease with rising temperature. In particular, this has beenproblematic for cleaning systems based on dissolved ozone. When ozonefunctions as an oxidant in water, e.g., to effect removal of materialfrom a surface, it can be counter productive to increase the intrinsicreaction rate of the ozone by increasing temperature. That is, when theintrinsic rate increases, the overall speed at which the system operatesto remove material does not increase and may decrease, due to reducedsolubility of the oxidant at elevated temperature.

In the semiconductor industry many manufacturing steps involvephotolithography. Photoresist is commonly patterned and etched on anexposed surface of a partially fabricated semiconductor wafer in orderto transfer a feature from a photomask to the surface. The feature,defined in the photoresist, is then transferred into the wafer materialthrough, for example, a selective etch process. By way of illustration,this technique is commonly used to define zones for ion implantation,shallow trench isolation, polysilicon interconnect and Damascenetrenches for metallization schemes.

After the PR is patterned and etched, and after the patternedphotoresist is used to etch the feature, it is necessary to removephotoresist or byproducts of the reactions. Conventionally, this hasbeen accomplished with a cleaning process based on reaction of ozonewith the material to be removed. For example, in a batch process, agroup of wafers may be dipped in a solution of water and ozone, possiblyunder agitation, to effect the removal.

It is generally recognized that the reaction rate for ozone removal ofPR and associated byproducts from a wafer surface is limited bydiffusion of O₃ to near the water/PR interface. Recently it has beenobserved that the rate of removal can be increased by first placing thewafers in a chamber of elevated temperature. With the wafers positionedabove a pool of heated water, water vapor condenses upon the wafersurfaces while O₃ is introduced into the chamber. In contrast toperforming the reaction while the wafers are immersed in a bath ofozonated water, the wafers above the pool have a limited thickness ofwater on the surfaces. Since the PR strip rate is limited by diffusionof O₃ through the DI water, providing a relatively thinner layer ofwater for a given partial pressure of O₃ gas increases the net amount ofO₃ diffusion to the water/PR interface; and this will result in anincreased reaction rate relative to the reaction rate which would resultwhen the ozone diffuses into a bath of water to reach the PR.

Nonetheless, with both the solubility and the diffusion of the reactantspecies so limited, the approach of placing wafers over a pool of waterto diffuse the species through condensate, at best, provides arate-limited reaction. If the diffusion rate and overall rate ofmaterial removal could be further increased, significant economies maybe made available. Specifically, PR removal in a single wafer processingsystem would become more cost effective.

SUMMARY OF THE INVENTION

According to one embodiment of the invention, the removal of material inreactions having limited solubility and diffusion of gaseous materialcan be increased by controlling the thickness of the layer into whichthe reactant species diffuses. In another embodiment, the thickness ofthe layer and the diffusion of the gaseous material can be individuallycontrolled. Apparatus and method are provided.

A flow apparatus is provided for removal of material from a work piecehaving at least one reaction region containing the removable material.The apparatus may include first and second assemblies positionable inspaced-apart relation to form a zone extending between the twoassemblies for movement of gaseous material. The first assembly mayinclude a fixture portion positioned to receive the work piece with thereaction region of the work piece disposed in the zone to allow movementof the gaseous material thereover. A flow assembly is configured totransfer into the zone a gas comprising a condensable material and areacting species.

According to another embodiment a system is provided for removal ofmaterial from a workpiece having at least one surface region containingthe removable material. The system includes a chamber, a flow componentand a support apparatus. The flow component is configured to passgaseous material into the chamber at a selectable rate and allow exit ofliquid and gaseous materials from the chamber. The support apparatus isconfigured to position the workpiece thereon with the surface region ofthe work piece oriented for contact with gaseous material passed intothe chamber by the flow component. The system may further include athermal control configured to provide a differential temperature betweena portion of a work piece positioned on the support apparatus andgaseous material passed into the chamber by the flow component.

A method for chemical processing is also provided wherein the thicknessof a layer of condensate on a surface is actively controlled and areactant species is diffused from a gaseous region overlying the surfaceinto the layer. According to an exemplary embodiment for removal ofmaterial from a work piece having at least one surface region containingthe removable material, a workpiece is placed in an atmospherecomprising a condensable gas and a reacting species. The partialpressure of the condensable gas is controlled to limit the formation ofliquid condensation on the surface region.

According to a method for removing unwanted material from the surface ofa semiconductor wafer, the wafer is placed in a zone having acontrollable atmosphere and gaseous materials including a gaseousreactant and a condensing vapor are passed into the zone for contactwith a wafer surface having the unwanted material thereon. The partialpressure of the condensing vapor in the zone is controlled to condensethe vapor on the wafer surface at a selectable rate and cover theunwanted material with a condensate layer of desired thickness. Thegaseous reactant is allowed to dissolve in the condensate.

In another embodiment for removing unwanted material from the surface ofa semiconductor wafer, the wafer is placed in a chamber, gaseousmaterials including an oxidant and a condensing vapor are passed intothe chamber for contact with a surface of the wafer having the unwantedmaterial thereon, and vapor is condensed on the wafer surface at apredeterminable rate to cover the unwanted material with a layer offluid. The oxidant is allowed to diffuse into the fluid at a selectablerate.

The foregoing background and summary have outlined general features ofthe invention. Those skilled in the art may acquire a betterunderstanding of the invention and the preferred embodiments withreference to the drawings and detailed description which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention will be acquired from thedetailed description which follows. When read in conjunction with theaccompanying drawing, in which FIG. 1 illustrates in schematic form anexemplary embodiment of a system for removal of material from a workpiece. Features presented in the drawing are not to scale.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of the invention are schematically illustratedwith reference to FIG. 1, wherein a flow system 10 is configured toremove material from a work piece. In this example the work piece is apartially fabricated semiconductor wafer 12 which may be of the type,for example, on which high density integrated circuits are formed. Thewafer 12 includes at least one reaction region 14 on a surface 16thereof. The region 14 contains material which is to be removed as partof a conventional photoresist pattern and etch sequence duringsemiconductor manufacture. It should be understood that several of thedesign features now illustrated are exemplary and only specific to thetype of work piece and the type of material to be removed from theregion 14. Further, the chemical materials chosen to perform theoperation are exemplary and numerous variants will be apparent based on,for example, the desired reaction rate, preferred values of reactionvariables, the material to be removed and features specific to the workpiece. In the illustrated example the material being removed from thereaction region 14 is photo resist and byproducts thereof, e.g., CO₂.The system 10 may be used for removal of other materials, includingatmospheric contaminants and various hydrocarbons, which may form on thesurface 16.

In the system 10 the work piece wafer 12 is placed in a zone 20 whichreceives a flow of gaseous material 22 (indicated with arrows) injectedtoward the central portion 24 of the wafer surface 16. The reaction isbased on dissolution of gaseous ozone in deionized water. Preferably,the ozone is delivered near the reaction region 14 by condensing watervapor (e.g., ten monolayers of H₂O under steady state conditions) on thewafer surface 16 and allowing ozone to diffuse into the H₂O. Althoughthe invention is not limited by any specific theory on the mechanisms ofthe desired reaction, it is believed that the presence of sufficient O₃in water effects a reaction which results in dissolution of photo resistmaterial and associated byproducts. The system 10 facilitates suchremoval in a rapid and controllable manner.

The system 10 includes a rotatable upper assembly 30 having a planesurface 32 and a rotatable lower assembly 34 including a fixture portion35 for holding the wafer 12 along a plane 36. The plane 36 is indicatedwith a hatched line. The surface 32 and the plane 36 are in aspaced-apart relation. Preferably the distance between the plane surface32 and the plane 36 is adjustable as notationally indicated by the arrow38. With the wafer 12 mechanically secured to the fixture portion 35 ina conventional manner, the zone 20 largely corresponds to a volumebetween the surface 32 and the plane 36, extending, more or less, to theperiphery 38 of the mounted wafer.

A wafer heating assembly provides thermal control of the wafertemperature. The heating assembly includes a thermal sensor 42positioned to monitor the wafer temperature. The illustrated sensor ispositioned for contact with the wafer in order to provide a calibratedelectrical signal indicative of the wafer temperature. The temperaturedependent signal generated by the sensor 42 is transmitted to acontroller 44, e.g., by wire or radio signal, and the controller 44regulates thermal input to the wafer 12 from one or more energy sources46. Sources 46 may, for example, be an array of thermal elements whichradiate infrared energy to the wafer 12, or they may be diode laserswith appropriate lens systems to direct the radiation to the wafer 12.

The gaseous material 22 is generated by an ozonating supply system 50.From the system 50 a mixture of water vapor and ozone is selectivelytransmitted through a feed line 52 for injection through the surface 32to direct the gaseous material 22 into the zone 20 at or near the centerportion 24 of the wafer 12. Movement of the material 22 into the feedline is through a valve 56 whose position is set by the controller 44.After entering the zone 20, a portion of the water vapor condenses onthe wafer surface 16 and, wafer surface 16 toward the wafer peripheryand exits the zone 20. Although not illustrated, texture orflow-enhancing paterns maybe formed along the surface 32 to facilitatedesired movement of the mixture 22 along the wafer surface 16.

During operation of the flow system 10 a wafer 12, containingphotoresist material to be removed from the reaction region 14, ispositioned in the lower assembly 34 along the plane 36 so that the wafersurface 16 is spaced apart from the surface 32 of the upper assembly 30.With this arrangement the distance between the wafer surface 16 and thesurface 32 may be adjusted by movement of one or both assemblies 30 and34 to select an appropriate volume for the zone 20. Preferably, thevolume of the zone 20 is determined for a prescribed flow rate,temperature and mix of the gaseous material 22 being injected into thezone 20. The flow rate should be selected so that the partial pressuresof ozone and water vapor over the reaction region 14 are predominantly afunction of the flow rate and properties of the injected gases,including any carrier gases incorporated in the material 22. Under theseconditions the partial pressures of the ozone and the water vapor arerelatively independent of pressure and temperature conditions outsidethe zone. Thus the zone 20 can develop conditions different from thoseof the adjoining atmosphere.

The temperature of the wafer surface and the resulting thin layer ofcondensed water formed on the surface 16 may be largely influenced bythe temperature of the wafer. On the other hand, the temperature ofgases in the zone 20 and above the condensed water will predominantlyresult from adjustments imparted to the material 22 by the heaterassembly 54 as directed by the controller 44.

Under these conditions the zone 20 provides an atmosphere comprising acondensable gas, e.g., water vapor, wherein the temperature of the gasrelative to the wafer surface 16 is controllable to influence the rateof condensation on the surface 16. Ozone or another gaseous reactant maydiffuse into the condensation at a rate controllable by the partialpressure of the gaseous reactant. With sufficient ozone dissolved in thecondensation, photoresist material is chemically removed from thereaction region 14. Although this removal process is understood toinclude diffusion of an oxidant such as ozone into the condensed layer,operation of the flow system 10 to effect such removal may not validateor depend upon any specific theory to describe a removal mechanism forthe unwanted material.

The rate of reaction may be enhanced with radiation. For example, asillustrated in FIG. 1, with ozone as the oxidant, the wafer surface 16may be irradiated with one or more ultra violet sources 62 positionedabove the plane surface 32. To effect transmission of the radiation tothe ozonated condensate on the surface 12, the surface 32 and othercomponents may be formed of fused silica or other material having asuitably high transmission for the radiation.

Spinning of the wafer 12 provides another means of controlling thethickness of the fluid layer and facilitates movement of condensate(carrying reaction products) off the wafer. This in turn accelerates thedevelopment of new condensate near the reaction site and diffusion ofmore ozone therein. The overall effect is to further improve the removalrate of material at a temperature and speed suitable for volumemanufacture of semiconductors and other products.

Once the reaction is under way or substantially complete, the flowvelocity and condensation rate of the gaseous mixture can be modified toincrease the rate at which material is rinsed off the surface 16. Forexample, removal of such may be enhanced by initially increasing therate of condensation on the surface and increasing the spin rate of thewafer 12. The volumetric flow rate of the gaseous mixture from thecenter portion 24 to the wafer periphery 38 may be increased bydecreasing the distance between the plane surface 32 and the plane 36.The temperature of the wafer surface 16 can be lowered relative to thetemperature of the gaseous material 22 in order to increase thecondensation rate. That is, the controller 44 may cut off thermal inputto the wafer 12 from the energy source 46 while increasing thetemperature of the gaseous material so that the surface 16 is at a lowertemperature than the temperature of the gaseous material 22.

The wafer may be dried by altering the composition of the gaseousmaterial 22 provided by the supply system 50 from water vapor and ozoneto a relatively inert gas such as nitrogen. The nitrogen may be passedover the wafer surface at a high flow rate while both the wafer 12 andthe upper assembly surface 32 spin. The flow rate of the nitrogen can bereadily increased by bringing the surface 32 closer to the plane 36. Thenitrogen may be heated under the direction of the controller 44 toenhance vaporization of the condensate. The controller can also turn onthermal input to the wafer 12 from the energy source 46 to increase therate of evaporation.

A feature of the invention is the ability to control and increase therate of a diffusion limited reaction which heretofore has been limitedby the thickness of the condensate layer into which the gaseous reactantis dissolved. By actively controlling the thickness of the condensatelayer the concentration of gaseous reactant in the condensate may berapidly increased. An exemplary means of effecting this increaseddiffusion rate has been illustrated, e.g., by effecting independentcontrol of wafer temperature and gas temperature over the wafer, or bycontrolling pressure in the zone 20, thereby modifying the relativehumidity that controls the thickness of the layer of condensate (e.g.,water on the wafer surface). The condensation rate can be controlled andlimited to maximize the reaction rate.

In the disclosed embodiment the gaseous reactant is an oxidant. Severalvariables controlling the state conditions of the oxidant, e.g., O₃, maybe modified to adjust the rate at which the oxidant reacts with theunwanted material, e.g., PR. The variables include temperature at thepoint of reaction (which may be varied by warming or cooling the wafersurface) and partial pressure of O₃ (which may be varied by modifyingthe net gas concentration or the pressure in the zone 20).

Generally the invention as disclosed may be performed in a chamber. Inthe illustrated embodiment of the flow system 10, the chamber is a zone20 open to atmospheric conditions, but capable of accommodating stateconditions different from the adjoining atmosphere. In a conventionalclosed chamber, e.g., one wherein the enclosed environment is sealedfrom the atmosphere, pressure can be varied by controlling the rate atwhich gas exits the chamber relative to both the volume of gas enteringthe chamber and the net volume increase due to by-products formed in thechamber. However, for the zone 20, as described with reference to FIG.1, the distance between the upper assembly surface 32 and the wafer 12can be adjusted to vary state conditions such as pressure in the zonewithout having to modify the temperature, composition or volumetric flowrate of gaseous material injected to the zone 20.

Thus vapor condensation rate can be controlled independent ofpredominant state conditions in the chamber vessel, e.g., zone 20 tovary the thickness of the fluid layer and maximize the diffusion rate ofthe reactant, e.g., ozone, into the condensed fluid. Another means ofestablishing conditions under which the rate of condensation iscontrolled is to inject a liquid 72, such as water, from a reservoir 70into the feed line 52. A valve 74, permitting movement of the liquidinto the feed line 52, is governed by the controller 44. The controller44 elevates the liquid to a desired temperature as the liquid passesthrough the heater assembly 54 so that the liquid 72, upon entry to thezone 20, undergoes thermal interaction with the wafer surface 16 whilethe wafer spins. Once the surface 16 reaches a desired temperature thecontroller closes the valve 74 and opens the valve 56 so that gaseousmaterial is injected through the feed line 52 at a different, e.g.,higher, temperature than that of the liquid 72. This process could becyclic in order to sustain optimal temperature differentials andperiodically wash reacted material off the surface 16.

The rate at which the wafer 12 is heated can be further increased with asupplemental feed assembly 80 comprising a feed line 82, a heater 84 inthe feed line 82, under direction of the controller 44, and a reservoir86 providing a liquid 88 into the feed line for transmission through theheater 84 and to the wafer 12. The liquid, e.g., water, is sprayed uponthe undersurface 90 of the wafer 12 for thermal transfer. The controller44 regulates movement of the heated liquid 88 with a valve 90. Variousliquids (including condensate containing removed material, liquid 72 andliquid 88) are permitted to collect in a drain region 92 for removal.

Generally the diffusion rate is controllable by the relative pressuresof the vapor and the reactant gas as well as the overall chamberpressure. Further, with the heater assembly 54 placed exterior to thechamber, e.g., outside of the zone 20, the temperature of the gaseousmaterial 22 and wafer temperature are individually controllable.Although not illustrated, further control can be had over the reactionby individually injecting the condensable vapor and the gaseous reactantinto the chamber in order to individually control their respectivetemperatures.

It should also be noted that the condensate need not be pure water.Other fluids such as methanol may be suitable and various mixtures,including those formed with inert materials, may be most useful in thisapplication.

A system and method have been provided wherein the condensation rate ofa vapor such as water can be controlled while separately controlling thereaction rate of an oxidant which dissolves in the condensed vapor. Thevapor pressure of the reacting species can be modified relative toatmospheric pressure as well as the vapor pressure of other gaseousmaterial in the chamber, e.g., the zone 20. The chamber gasconcentration of the condensing vapor and the reacting species, and thetemperature of the work piece surface, are all adjustable to control theoverall rate at which the species, e.g., ozone, reacts with material onthe surface of the work piece. The condensable vapor and the reactingspecies can be selectively directed to the work piece. In the case wherethe work piece is a semiconductor wafer, the gaseous materials aredirected toward a center portion of the work piece such that they mayflow toward the periphery as they exit the chamber.

The invention has been described with only a few illustrativeembodiments while the principles disclosed herein provide a basis forpracticing the invention in a variety of ways. Although the disclosedsystems and methods have been illustrated for semiconductormanufacturing applications, the concepts are generally applicable toremoval of materials from surfaces with reactant species that diffusethrough a layer. Other constructions, although not expressly describedherein, do not depart from the scope of the invention which is only tobe limited by the claims which follow:

What is claimed is:
 1. A flow apparatus for removal of material from awork piece having at least one reaction region containing the removablematerial, the apparatus comprising: first and second assemblies within ahousing positionable in spaced-apart relation to form a zone extendingbetween the two assemblies for movement of gaseous material, the firstassembly including a fixture portion positioned to receive the workpiece with the reaction region of the work piece disposed in the zone toallow movement of the gaseous material thereover, the second assemblyincluding a flow assembly configured to transfer into the zone, directlyfrom a position over the fixture portion, a gas comprising a condensablematerial and a reacting species; and controls for modifying the stateconditions within the zone relative to the state conditions in otherregions within the housing.
 2. The apparatus of claim 1 wherein thefixture portion is positioned to receive the work piece along a planeand the second assembly includes a surface spaced apart from the planeso that the zone extends between the plane and the second assemblysurface.
 3. The apparatus of claim 2 wherein the zone is bounded by theplane and the second assembly surface.
 4. The apparatus of claim 1wherein the zone is open to the atmosphere.
 5. The apparatus of claim 4wherein state conditions within the zone are isolated from theatmosphere when the flow assembly transfers the gas into the zone underconditions which result in removal of the material from the reactionregion.
 6. The apparatus of claim 1 further including a thermal assemblyconfigured to selectively elevate the temperature of a work piecereaction region positioned in the zone.
 7. The apparatus of claim 1further including a thermal assembly configured to selectively elevatethe temperature of a work piece reaction region positioned on thefixture portion relative to the temperature of gas transferred into thezone by the flow assembly.
 8. The apparatus of claim 1 further includinga thermal control configured to selectively adjust the temperature of awork piece reaction region positioned in the zone and the temperature ofthe gas entering the zone relative to one another.
 9. The apparatus ofclaim 1 further including a system for generating gaseous materialcomprising ozone and water vapor coupled to transmit the gaseousmaterial to the flow assembly for injection through the zone.
 10. Theapparatus of claim 1 wherein the second assembly includes a surfacespaced apart from the fixture portion to define the zone in a regionbetween the second assembly surface and a work piece positioned on thefixture portion so that vapor pressure in the zone is controllable bymodifying the distance between the second assembly surface and the workpiece.
 11. The apparatus of claim 1 wherein the vapor pressure in thezone is controllable by modifying the volumetric flow rate of gaseousmaterial entering the zone.
 12. The apparatus of claim 1 wherein theflow assembly includes a feed line configured to transmit the gaseousmaterial through the second assembly and direct flow of the gaseousmaterial from a central portion of the work piece to an outer portion ofthe work piece.
 13. The flow apparatus of claim 1 wherein the controlsfor modifying the state condition in the zone include a controller formodifying the flow velocity and condensation rate of the gas.
 14. Asystem for removal of material from a work piece having at least onesurface region containing the removable material comprising: a chamber;first and second assemblies within the chamber positionable inspaced-apart relation to form a zone extending between the twoassemblies for movement of gaseous material, the second assemblyincluding a flow component configured to pass gaseous material into thechamber at a selectable rate and allowing exit of liquid and gaseousmaterials from the chamber, the first assembly including supportapparatus configured to position the work piece thereon with the surfaceregion of the work piece oriented for contact with gaseous materialpassed into the chamber by the flow component; and a thermal controlconfigured to provide a selectable differential temperature between aportion of the work piece positioned on the support apparatus andgaseous material passed into the chamber by the flow component; andcontrols for modifying the state conditions within the zone relative tothe state conditions in other regions within the chamber.
 15. The systemof claim 14 wherein the thermal control system includes an energy sourceconfigured to elevate the temperature of the work piece relative toanother temperature in the chamber.
 16. The system of claim 14 whereinthe thermal control system includes a heater coupled to elevatetemperature of gaseous material prior to being passed into the chamber.17. The system of claim 14 wherein the flow component includes a feedline extending toward the support apparatus so that when the work pieceis positioned on the support apparatus gas discharged from the feed lineflows along the surface region.
 18. The system of claim 14 wherein theflow component includes a feed line extending toward the supportapparatus so that, when the work piece is positioned on the supportapparatus, gas discharged from the feed line flows directly toward thesurface region, said system further including a flow control memberpositionable along the surface region to direct flow of gaseous materialalong the work piece surface region.
 19. The system of claim 14 whereinthe chamber is a region defined in part by a flow control surface spacedapart from the support apparatus.
 20. The system of claim 19 wherein thesupport apparatus is configured to receive a work piece along a planeand the flow control member includes a plane surface positioned todefine a region between the plane surface and a positioned work piecethrough which gaseous material is transmitted to react with the surfaceregion.
 21. The system of claim 20 wherein the distance between apositioned work piece and the plane surface is variable.
 22. The systemof claim 14 wherein the flow component is capable of injecting a liquidof controllable temperature into the chamber for contact with the workpiece to thermally control the temperature of the work piece.